Printing electronic circuitry with copper nanoparticle ink and green
laser light can be more cost beneficial and efficient, according to a
study.

Researchers at Soonchunhyang University in South Korea studied the
thin-film printing technique instead of the conventional methods, based
on laser power, scanning speed, pre-baking conditions and film thickness
effects. Their findings were published this week in the journal AIP
Advances.

Nanoparticles in metallic inks have an advantage over bulk metals
because of their lower melting points in the circuitry manufacturing.

Originally the researchers, led by Kye-Si Kwon, tested silver
nanoparticle ink but found it is costlier. Then, they studied studied
copper, which is derived from copper oxide.

Although copper's melting point of copper is nearly 2,000 degrees
Fahrenheit, copper nanoparticles can be brought to their melting point
at just 300 to 930 through sintering. Then, they can be merged and bound
together.

The nanoparticles are heated by the absorption of light.

"A laser beam can be focused on a very small area, down to the micrometer level," the researchers said.

Heat from the laser converts copper oxide into copper and promotes the conjoining of copper particles through melting.

The researchers decided a green laser -- in the 500- to 800-nanometer
wavelength absorption rate range -- would be ideal for their purposes.
And because green lasers in this role have not been reported elsewhere,
Kwon wanted to see how it worked.

The researchers used commercially available copper oxide nanoparticle
ink that was spin-coated onto glass at two speeds to obtain two
thicknesses. They prebaked the material to dry out most of the solvent
before sintering to reduce the copper oxide film thickness and to
prevent air bubble explosions when the solvent suddenly boils during
irradiation.

They concluded that the prebaking temperature should be slightly lower than 400 degrees F.

In searching for optimal settings of laser power and scanning speed
during sintering, they worked to enhance the conductivity of the copper
circuits. The found the best results were produced with laser power from
0.3 to 0.5 watts. To reach the desired conductivity, the laser scanning
speed should be at least 10 millimeters per second and less than 100.